Recently, the development of the backbone network communication line as mainly focusing on the optical fiber communication technology is proceeding steadily and, in such a situation, the electronic wirings in the information terminal are becoming a bottleneck. Against, such background, instead of the conventional electric circuit substrate in which all signal transmissions are made by using the electric signal, the optoelectronic composite substrate (optical waveguide device) of the type that transmits high-speed parts by the light has been proposed, in order to compensate the limit of transmission speed of the electric signal.
In the optoelectronic composite substrate, the light signal is transmitted by the optical waveguide having a structure in which the core layer is surrounded by the cladding layers. Then, the light path is converted at 90° by the light path conversion portion provided to the end part of the optical waveguide.
The related arts are disclosed in Japanese Laid-open Patent Publication No. 2009-20391 and In Publication Pamphlet. No. WO 2003/58305, and Japanese Laid-open Patent Publication. No. 11-24894.
In the optical waveguide device, a plurality of emitting portions of the emitting element are optically coupled to light entering portions of respective light paths of the optical waveguide respectively, and the lights are emitted from the respective emitting portions to the respective light entering portions respectively. Here, the light being emitted from the respective emitting portions of the emitting element is emitted to spread to the lateral, direction as well.
For this reason, particularly, in the case that the light paths of the optical waveguide are arranged at a narrow pitch, the lights being emitted from the emitting portion are entered to the adjacent light path as the unnecessary light. As a result, such a problem exists that the optical crosstalk is generated and thus degradation of the light signal is brought about.
Also, at the time when the lights are entered to the respective light receiving portions of the light receiving element, from the light emitting portions of the respective light paths of the optical waveguide respectively as well the similar optical crosstalk is easily caused due to the reflected light from the light path conversion portion.